1. Field of the Invention
The present invention relates generally to a pump which will provide moving force for fluid flow of liquids without subjecting the liquids to substantial mechanical shear stresses. More particularly, it relates to such a pump which is especially suited for pumping liquids used in biochemical procedures, such as fragile proteins and/or cell suspensions, and other liquids subject to damage if subjected to substantial mechanical shear stresses in fluid flow.
2. Description of the Prior Art
It is known in the art to utilize a tube which is deformed by a roller or a plunger for the purpose of pumping liquids. Such pumps are disclosed, for example, in the following issued U.S. Pat. Nos.: 2,412,397, issued Dec. 10, 1946 to Harper; 2,963,014, issued Dec. 6, 1960 to Voelcker; 3,127,845, issued Apr. 7, 1964 to Voelcker; 4,182,465, issued Jan. 8, 1980 to Bennett; 4,222,501, issued Sept. 16, 1980 to Hammett et al. and commonly assigned 4,365,943, issued Dec. 28, 1982 to Durrum. Another form of pump intended for liquids subject to damage by mechanical shear is a pneumatically actuated membrane/hose pump, commercially available under the designation Steripump, from Steridose Systems AB, Gothenburg, Sweden.
While pumps of the type disclosed in these issued patents and the above commercial product have proved to be satisfactory for their intended applications, there is a continuing demand for pumps that will meet the stringent requirements of biochemical reagent and reaction product liquids. These liquids typically are pharmaceutical solutions having a high value per unit volume. Loss of these liquids by leakage would therefore be costly. Pumps and other equipment used to handle them must therefore be very reliable. A significant problem with prior art pumps utilizing distortion of a flexible tube to pump the liquids is the short lifetime of the tube as a result of creasing it. Prior art flexible tube designs as disclosed in the above patents result in creasing the tube or similar severe localized distortion as the tube is flexed to provide the pumping action. Such creasing or other severe localized distortion of the tube causes it to fail and leak after a short time. The biochemical liquids also contain very fragile long chain protein molecules or fragile cells in suspension and cannot be subjected to substantial mechanical shear stress during their fluid flow without being damaged. A need therefore remains for a pump that will meet the demands of these and other liquids that are subject to damage when subjected to mechanical shear stress.